1. Field of the Invention
The present invention relates to a 2-wire/3-wire converting apparatus which enables connection between a 2-wire interface provided in a data communication terminal etc. to be connected to a public telephone circuit and a 3-wire interface provided in an automobile telephone, a portable telephone, a cordless telephone etc.
2. Description of the Related Art
In a typical mobile communication system, as shown in FIG. 6, a mobile network control apparatus 4 is interposed for enabling connection between a mobile transceiver 2 for wireless communication with a telephone company 1 and a data communication terminal 3 such as a facsimile apparatus or a personal computer. The transceiver 2 is connected to the network control apparatus 4 through an interface 5 of the transceiver 2, an interface 6 of the network control apparatus 4, and a line 7. The interfaces 5 and 6 have 24 pins or 10 pins, respectively. The data communication terminal 3 is connected to the network control apparatus 4 through a 2-wire interface 8 of the terminal 3 for a public telephone circuit, a 2-wire interface 9 of the network control apparatus 4, and a line 10.
The foregoing system as shown in FIG. 6 entails provision of relatively large mobile network control apparatus 4, resulting in increasing the structure of the control apparatus 4 in size.
Another system is shown in FIG. 7. This system makes it possible to communicate a telephone company 1 with a portable telephone 11 or an automobile telephone by wireless. 12 denotes a 3-wire interface for connecting the handset of the portable telephone 11 to a data communication terminal 13. A 3-wire interface 12 is connected to a 3-wire interface 14 provided in the data communication terminal 13 through a line 15.
The data communication terminal 13 provided in the system shown in FIG. 7 includes the 3-wire interface 14 for connection with a 3-wire circuit which has three signal lines, one for transmission, one for reception, and one for common line. Hence, this data communication terminal 13 cannot be directly connected to the 2-wire telephone circuit having two bidirectional signal lines. This type of data communication terminal provided with a 3-wire interface is deemed to have a special specification in these days since a public telephone circuit modular specification based on the use of the 2-wire interface has been generalized. Hence, it is quite disadvantageous today to use such a data communication terminal provided with a 3-wire interface.